1. Field of the Invention
The present invention relates to a reciprocating pump and a check valve, and more particularly to a reciprocating pump that is capable of discharging gas therefrom and a check valve used for the reciprocating pump.
2. Related Art
A reciprocating pump for delivering fluid by driving a diaphragm has been hitherto known, which is generally designed to convert rotational motion produced by a driving means such as a motor into linear motion via a cam so as to drive the diaphragm by this linear reciprocating motion. A more specific construction hitherto known is that linear reciprocating motion based upon a motor or the like is transmitted to the diaphragm via operating fluid as an operating medium.
The thus constructed reciprocating pump is so operated that an elastically deformable diaphragm is reciprocated by using operating fluid, which reciprocating motion causes suction and discharge of fluid to be delivered (target fluid). In order to achieve the required degree of elastic deformability and reciprocating motion, the diaphragm is formed with a thinner wall.
The above conventional reciprocating pump, which is constructed by using such a thin diaphragm, may cause undesirable deformation or cracks of the diaphragm, or any other damage thereto due to excessive load applied to the diaphragm.
A known reciprocating pump, which employs a technique to prevent such a deformation or clack of the diaphragm, is disclosed in for example Japanese Patent Application Laid-open No. Sho-61-61990 (Reference 1). The disclosed reciprocating pump is provided with a valve unit which is operated along with the diaphragm so that the valve unit limits the motion of the diaphragm and hence controls inflow of operating fluid before excessive load is applied to the diaphragm.
In a fluid delivery passage according to a prior art arrangement, a check valve, which is made up by using a ball or the like, is provided so as to prevent reverse flaw of the target fluid. Particularly, for delivering high viscous fluid (sticky fluid), a know construction as disclosed in for example Japanese Patent Application Laid-open No. 2000-356274 (Reference 2) employs an urging member such as a spring for moving the ball so as to securely close a fluid passage. That is, when delivering high viscous fluid, frictional resistance is caused on the ball serving as a valve element, which in turn causes delay in seating the ball, during which delay fluid reversely flows in the passage. As a result, the discharge rate of the pump is decreased, thus affecting on the performance of the pump to constantly deliver fluid. Therefore, as described above, the urging member such as a spring is provided on an upper portion of the ball so as to enhance smooth seating of the ball in the conventional arrangement.
However, the conventional reciprocating pump as disclosed in the Reference 1 requires a relief valve (escape valve) for controlling a flow of operating fluid and a degassing member (discharge valve) for removing gas such as air mixed into or generated in operating fluid, and therefore has a problem of causing troublesome work particularly in degassing operation by using this degassing member.
Since the above conventional reciprocating pump is so designed to make the diaphragm reciprocate by means of operating fluid, gas such as air may be mixed into operating fluid during assembling or driving the pump. It is desirable to avoid such mixing of gas into operating fluid in the reciprocating pump having an arrangement with the diaphragm reciprocated by operating fluid. For the purpose of avoiding this, the conventional pump employs a degassing mechanism (a degassing member) provided between the diaphragm and the valve unit so as to properly remove gas in an initial operation subsequent to assembling of the pump and at the time when gas intrudes during the drive of the pump.
The degassing operation by using the above mechanism involves removing a lid member such as a bolt disposed on the degassing member and bringing a suction device or the like into communication with this degassing member. During this degassing operation, operating fluid may overflow from the degassing member along with gas, and therefore an oil pan or the like must be disposed around the degassing member.
Also, gas, which has been mixed into along with operating fluid, may be removed from the relief valve provided near the valve unit. However, in the prior art technique as disclosed in the Reference 1, the construction of the relief valve cannot be ascertained from the disclosure of this Reference so that the relationship between adjustment of operating fluid and degassing cannot be clearly understood.
That is, according to the prior art technique, of the degassing member for gas removal and the relief valve for resultingly achieve degassing, the former involves a troublesome work in gas removing operation, and the latter is of an unknown construction not designed for positive degassing operation, and therefore poses a problem that its effect cannot be clearly expected.
Also, in the check valve according to the prior art technique as disclosed in the Reference 2, the movement of the ball as a valve element is enhanced by the urging member such as a spring so as to securely close the flow passage. This arrangement causes increased resisting force between the valve element and a valve seat and hence cavitation during a suction step, which may deteriorate the pumping performance. Also, when a spring or the like exerting a strong spring force is used, it is necessary to prime fluid into the pump before actuating the pump due to lack of self-feeding of fluid. As another problem, the pressing force, which presses the ball against the valve seat by the spring or the like for closing the flow passage, may cause local or uneven wear-out of the ball, valve seat or the like.
In case of using the reciprocating pump according to the prior art technique for delivering high viscous fluid (sticky fluid), it also causes a problem that fluid cannot be delivered at a constant rate in a proper manner even if the check valve or the like is employed. Specifically, if fluid has high viscosity, fluid is hard to flow, with the result that it cannot be properly sucked by driving the diaphragm or any other reciprocating means, only. Thus, fluid delivery at a constant rate is hardly achieved.
Therefore, it is an object of the present invention to provide a reciprocating pump equipped with a gas discharge mechanism that is capable of properly and automatically discharging gas without a troublesome work involved.
It is another object of the present invention to provide a valve seat that is capable of securely closing a fluid passage, while reducing local or uneven wear-out of a ball or the valve seat itself without the necessity to prime fluid.
It is still another object of the present invention to provide a reciprocating pump that is capable of delivering fluid at a constant rate even if fluid has high viscosity.